package com.zoshine.zzg.util.idworker;


/**
 * 雪花算法id生成器
 *
 * @author 贾俊峰
 * @time 2017/6/20 11:10
 */
public class SnowflakeIdWorker implements IdWorker<Long> {

    /** 开始时间戳(2017-06-20) */
    private static final long EPOCH = 1497888000000L;
    /** 机器id所占的位数 */
    private static final long WORKER_ID_BITS = 5L;
    /** 数据中心id所占的位数 */
    private static final long DATA_CENTER_ID_BITS = 5L;
    /** 支持的最大机器id，结果是31 (这个移位算法可以很快的计算出几位二进制数所能表示的最大十进制数) */
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    /** 支持的最大数据标识id，结果是31 */
    private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);
    /** 序列在id中占的位数 */
    private static final long SEQUENCE_BITS = 12L;
    /** 机器ID向左移12位 */
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;
    /** 数据中心id向左移17位(12+5) */
    private static final long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    /** 时间戳向左移22位(5+5+12) */
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS;
    /** 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095) */
    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);

    /** 工作机器ID(0~31) */
    private long workerId;
    /** 数据中心ID(0~31) */
    private long dataCenterId;
    /** 毫秒内序列(0~4095) */
    private long sequence = 0L;
    /** 上次生成ID的时间戳 */
    private long lastTimestamp = -1L;

    /**
     * 构造器
     *
     * @param workerId     工作id(0~31)
     * @param dataCenterId 数据中心id(0~31)
     */
    public SnowflakeIdWorker(long workerId, long dataCenterId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID));
        }
        if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
            throw new IllegalArgumentException(String.format("data center Id can't be greater than %d or less than 0", MAX_DATA_CENTER_ID));
        }
        this.workerId = workerId;
        this.dataCenterId = dataCenterId;
    }

    @Override
    public Long createId() {
        return nextId();
    }

    /**
     * 获取下一个id(该方法是线程安全的)
     *
     * @return 下一个id
     */
    private synchronized long nextId() {
        long timestamp = timeGen();

        //如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过，这个时候应当抛出异常
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        if (lastTimestamp == timestamp) { //如果是同一时间生成的，则进行毫秒内序列
            sequence = (sequence + 1) & SEQUENCE_MASK;
            //毫秒内序列溢出
            if (sequence == 0) {
                //阻塞到下一个毫秒,获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else { //时间戳改变，毫秒内序列重置
            sequence = 0L;
        }
        //上次生成ID的时间戳
        lastTimestamp = timestamp;
        //移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - EPOCH) << TIMESTAMP_LEFT_SHIFT) | (dataCenterId << DATA_CENTER_ID_SHIFT) | (workerId << WORKER_ID_SHIFT) | sequence;
    }

    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     *
     * @param lastTimestamp 上次生成ID的时间戳
     * @return 新的时间戳
     */
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    /**
     * 返回当前时间戳
     *
     * @return 当前时间戳(毫秒)
     */
    private long timeGen() {
        return System.currentTimeMillis();
    }


    /**
     * 测试方法
     */
    public static void main(String[] args) {
        IdWorker<Long> idWorker = new SnowflakeIdWorker(1, 1);
        Long newId = idWorker.createId();
        System.out.println("生成的id:"+newId);


//        // 下面是测试多线程安全的
//        Set<Long> set = new ConcurrentSkipListSet<>();
//        CountDownLatch count = new CountDownLatch(1000);
//        AtomicInteger atomicInteger = new AtomicInteger(0);
//
//        long l1 = System.currentTimeMillis();
//        // 启动1000个线程，每个线程生成1000个id
//        for (int i = 0; i < 1000; i++) {
//            Thread thread = new Thread(() -> {
//                for (int j = 0; j < 10000; j++) {
//                    long id = idWorker.createId();
//                    if (set.contains(id)) {
//                        System.out.println("contains id:" + id);
//                    }
//                    set.add(idWorker.createId());
//                    atomicInteger.addAndGet(1);
//                }
//                count.countDown();
//            });
//            thread.start();
//        }
//        try {
//            count.await();
//        } catch (InterruptedException e) {
//            e.printStackTrace();
//        }
////        for (Long id: set) {
////            System.out.println(id);
////        }
//        // 如果打印出的两个值相等，说明线程安全
//        long l2 = System.currentTimeMillis();
//        System.out.println("共计生成id："+ atomicInteger.intValue() + "个");
//        System.out.println("用时："+(l2-l1)+"毫秒");
    }
}
